A fluorometer is an instrument for detecting and, usually, measuring fluorescence. Some substances, for example hydrocarbon substances such as oil, exhibit a natural fluorescence. Other substances may be provided with a fluorescent agent, or tracer, such as fluorescein. A typical fluorometer includes an excitation source, for causing fluorescence in a target substance, and a detector for measuring the resultant fluorescence.
It is known to employ fluorometers in the detection of leaks of fluorescent materials from underwater objects such as pipelines or risers. For example, U.S. Pat. No. 4,178,512 (Frungel) describes a fluorometer for measurements in deep water. The Frungel device comprises a flash lamp unit with detector system orientated at right angles to the lamp. However, the Frungel device is only capable of detecting fluorescent material within a few inches of the lamp/detector. To compensate for the very short range, or point nature, of the measurement, such devices can be used in vertical profiling or simply towed through the water at a varying depths. As a result, such devices may miss significant patches of the fluorescent target thereby giving a false picture of the distribution of the fluorescent species. Such devices are therefore considered to be very inefficient.
GB 2 089 501 (Conoco) discloses an apparatus for detecting hydrocarbons in a body of water, wherein the excitation source comprises a laser which scans the body of water to excite and detect fluorescent materials. The Conoco apparatus is reported as being particularly suited to detecting hydrocarbons on or near the sea surface from a range of several meters. However, because the apparatus is laser-based, it is bulky, expensive and requires a relatively large amount of power. Consequently, such apparatus have restricted use on ROVs (Remotely Operated Vehicles) and particularly AUVs (Autonomous Underwater Vehicles). Moreover, such apparatus suffer from the practicalities associated with health and safety issues surrounding lasers.
U.S. Pat. No. 6,255,118 (Alfano) discloses a fluorometer which employs an LED (Light Emitting Diode) excitation source. However, the LED excitation source is only suitable for exciting material held in a local sample cell. Such devices are not suitable for long range, or remote, detection, particularly underwater.
It would be desirable, therefore, to provide a fluorometer which is capable of remotely detecting fluorescent material, especially in an underwater environment, and which does not suffer from the problems outlined above.